1. Field of the Invention
The present invention relates to a method for forming a semiconductor device, and more particularly to, a method for forming a semiconductor device which can achieve a high capacitance in a small area by implementing a trench-type capacitor while using a conventional MPDL manufacturing process.
2. Description of the Related Art
As integration of a semiconductor device increases, the size of the cells gets smaller. Therefore, it is more difficult to form a capacitor having a sufficient capacitance. Particularly, in case of a DRAM device constructed with one MOS transistor and capacitor, word lines and bit lines are orthogonally arranged on a semiconductor substrate in longitudinal and transverse directions. The capacitor is formed across two gates and a contact hole is formed on the center of the capacitor. At this time, the above-mentioned capacitor is mostly made of a polycrystalline silicon layer as a conductive material and an oxide film, a nitride film or a laminated film thereof such as an ONO (oxide-nitride-oxide) film as a dielectric material. It is key key for high integration of a DRAM device to reduce the size of a chip while the capacitance, which occupies large area of a chip, is kept large.
FIGS. 1a to 1d are cross-sectional views for illustrating a method for forming a semiconductor device in accordance with the prior art.
Referring to FIG. 1a, a pad oxide film 11 and a nitride film 12 are deposited on a silicon substrate 10 and thereafter a trench structure having an angle of 77xc2x0 is formed thereon by photo etching and dry etching. Then, an oxide film 13 is deposited and insulation is provided by CMP planarization.
Referring to FIG. 1b, after performing an implant process for forming a well (not shown) and a cell Vt implant and capacitor Vt implant process are carried out. Then, a gate oxide film 14 for forming a gate is formed, a doped silicon 15 is deposited, and then a photoresist pattern 16 is formed.
Referring to FIG. 1c, a dry etching is performed using the photoresist pattern 16 as a mask to thus form a planer capacitor 17 and a gate 18.
Referring to FIG. 1d, after deposition of IPO (Inter Poly Oxide) 19, a metal contact is formed through photo etching and dry etching and then a bit line 20 is formed. By carrying out a wiring process, a MPDL cell is manufactured.
However, such a MPDL cell according to the prior art is problematic in that a capacitor area with a large area is required for implementing a higher capacitor value to secure an operation margin of a sensor and improve refresh characteristics by increasing the sensing margin.
The present invention is designed in consideration of the problems of the prior art, and therefore it is an object of the present invention to provide a method for forming a semiconductor device which increases capacitance by forming a structure of a trench capacitor and using an inner side face of the capacitor as a capacitor region.
To achieve the above object, there is provided a method for forming a semiconductor device in accordance with the present invention, comprising the steps of: depositing a pad oxide film and a nitride film on a silicon substrate, forming a 77 angle trench by photo etching and dry etching, depositing a HLD oxide film and then insulating the device; performing a cell Vt implant process on the resulting material and then forming a first photoresist pattern for adjusting the capacitor Vt; defining a capacitor region by performing dry etching using the HLD oxide film and the first photoresist pattern as a barrier layer; performing an implant process on the resulting material; forming a gate oxide film on the resulting material, depositing a doped poly and forming a second photoresist pattern; forming a trench capacitor and a gate by photo etching and dry etching using the second photoresist pattern; and depositing an interlayer film on the resulting material, planarizing the same, forming a metal contact and performing a bit line and wiring process thereon.
At this time, the dry etching process for defining the capacitor region is performed at 80 to 90 degrees.
After the defining the capacitor region, a cleaning process is performed with an ammonia-based cleaning solution.
By performing an additional dry etching process using the HLD oxide film and the first photoresist pattern as a barrier layer, four inside surfaces of the capacitor are all defined as the capacitor region to thus increase the capacitance of the capacitor.
When performing the implant process on the resulting material on which the capacitor region is defined, a tilt implant process is performed to implant a dopant evenly on the side faces and bottom of the trench capacitor.